This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 01 04 160 filed Mar. 28, 2001, the entire contents of which are incorporated by reference.
The invention relates to image acquisition methods by an X-ray radiography apparatus designed, in particular, for angiography.
In vascular imaging, in many cases, it is important to be able to identify the actual size of arteries from images from the X-ray radiography apparatus. This is because stenosis, a narrowing of the artery, is frequently treated by introducing a balloon into the artery and then by dilating the balloon to the size of the healthy artery. The size of the healthy artery is determined by measuring the artery on each side of the lesion due to the stenosis. This measurement is used to select a balloon of suitable size to treat the stenosis. The images from the x-ray radiographs are projections. Consequently, a magnification factor is determined to indicate the actual size of the artery from its size in the image. Several approaches have been proposed in order to calculate the magnification factor. One approach currently used is to locate a catheter (or any other object whose size is known) in the image and to determine its size in the image. The actual size of the object is entered into the apparatus. Thus, the magnification factor for the object is determined. Assuming that the distance to the projection center is similar for the object and for the artery, the same magnification factor is used to determine the size of the artery. This approach has several disadvantages. First, it requires the user to provide information which is not directly connected with the pathology, that is to say, the size of the instrument which is used as a calibration object. Should there be an error, a poor measurement is made. Second, the applied algorithm assumes that the calibration object and the artery to be measured are close to each other. This is almost never the case. Furthermore, in certain situations, when the user wishes to employ a catheter as a calibration object, the catheter is not necessarily visible on the image selected in order to measure the artery. This may lead to considerable errors of accuracy in determining the size of the artery, which is detrimental to the proper treatment of the stenosis.